A mook is commonly a fellow who tries hard to be normal but finds most things around him so boring that he can't pay attention. As a result he seems odd, and dumb as a fence post. Although it could be an annoying trait, if you told him about it, he would say: "I dunno". Their value to society is well documented.

Noun. A dumb male, typically young (18-30) and from the Northeast. Ignorant and garish, mooks are easily defined by one of a dozen characteristics listed in the examples below. Typically from Long Island or Northern New Jersey, mooks have spread into NYC, southern NJ, philly and boston. The capital of the mook world is the jersey shore in summer with spillover into atlantic city. Yankee stadium is (unfortunately) another cesspool of mooks. If you see a mook do not approach him, they are irrational and prone to violence. Simply observe from a distance, they are loud, you will not miss anything. If they approach you use simple generic phrases like "you see the game last night" or "im good bro" or "yeah ill be down at the shore this weekend" to dismiss them.
Other known names-
Benny or Bennie (bayonne, elizabeth, newark, new york)
Meathead
Ape
Gorilla
yellow tag (refering to NJ license plates)
631'r (long island area code)

hair gel
fake tans
Steriod use
Loudmouths- typically at sporting events and bars but not limited to these places (jersey shore, atlantic city, cheesey nightclubs, etc) The louder the place, the louder they get.
They love to fight- even without steriods
Baseball cap or visor in orientation other than straight forward
Italian (predominant but not exclusive)
Racist (towards everyone but themselves)
Man sluts- they will try to sleep with anything, especially skanks, mooks love skanks
Popped collars- especially on a pink polo shirt
Ed hardy Shirts/Affliction Shirts- A new craze amongst mooks
Striped Armani Club shirt- No mook is complete without their club shirt
Single letter gestures of communication; A- pronounced "eehhyyy"; O- Pronouced "ooohhhh"
Inflated sense of self worth- yes mooks think they are the greatest and everyone should love them
Leased 2 door BMW in black or white- Mooks may live with their parents but will still lease a BMW
Affinity for cheap beer- Mooks have no class and prefer the cheapest swill available. Most mooks also drink way too much.
There are many more but this should suffice if defining a mook. Remember these are bad people and should be avoided at all costs